The invention relates to the problem of adaptive data detection in a mobile radio receiver. "Adaptive" means that a device is provided in the receiver, which device can understand the time changes of the properties of the mobile radio channel. Such devices normally operate using the LMS (Least Mean Squares) (see for example, citation [1]), or the RLS (Recursive Least Squares) (see for example, citation [2]) algorithm. These algorithms adapt to the properties of the transmission channel continually with time.
EP-A-520 969 specifies an estimation method for data detection, in the case of which received samples in a time slot are initially stored and processed starting with the first received value, to be precise to beyond a fading incursion; further processing is then carried out, starting with the last stored sample, in order to produce estimated values of the transmitted data.
A Kalman filter for adaptation of the channel impulse response in a mobile radio receiver is described in Fifth European Signal Processing Conference, Sep. 18-21 1990, Barcelona, ES; Elsevier, Amsterdam, NL, 1990; pages 225-228, Morgul & Dzung: "New optimum recursive parameter estimation/detection using unreliable erasure declaring detectors". In this case, the Kalman algorithm is applied only to the channel impulse response which is present at a specific time.
The present patent application shows that the algorithms which are continuously adapted with time fail under certain conditions, which are typical for mobile radios. The reason for this is that such adaptation algorithms can be regarded as time-variant first order recursive filters. Higher order algorithms exhibit a behavior which is better in principle.